This invention relates to a variable velocity conveying method and apparatus for continuous motion saws and, more particularly to a skewed orbiting saw for transversely cutting continuously advancing elongated lengths of multi-ply material into shorter lengths.
This invention is an improvement on co-owned Patent RE 30,598 and reference may be had thereto for details of construction and operation not set forth herein. The '598 patent employed a saw moving through an orbit which was skewed to the direction of movement of the multi-ply material. One advantageous application has to with "logs" of convolutely wound paper such as are used for kitchen toweling and toilet tissue. In the manufacture of such household products, a web is unwound from a parent roll of five to nine feet in diameter and eight to eleven feet in axial length, transversely perforated and then rewound into a "log" having the diameter of the retail size roll. Thereafter, the elongated log is transversely severed into axial lengths corresponding to those found on the store shelves. This transverse cutting has been advantageously performed in the past by means of orbiting log saws. Also such orbiting log saws have been employed to separate elongated stacks of interleaved web material such as facial tissues and toweling. The above-identified '598 patent represented a major breakthrough because prior to the skewed orbit saw, the saw operation had to be limited while the log was indexed past the saw for the next cutting position. By using the skewed orbit, the log could be advanced continuously because the saw traveled with the log during the cutting operation. The producers of wound superimposed plies such as toilet tissue and toweling logs and stacked superimposed plies such as folded tissue and toweling are continually demanding increased efficiency which includes reduced down-time for maintenance such as that to correct infeed product conveyor chain wear and also for product changeover such as various cutoff lengths. These problems have not been solved by the current state of the art and the invention herein described does solve these problems.
For example, as the infeed product conveyor chain wears, the velocity profile can be altered by pushbutton to compensate for it. As the cutoff requirements change based on various product or marketing demands, the velocity profile of the infeed product conveyor can be changed by pushbutton. An added advantage to the non-uniformly advancing of material is the ability to reduce or eliminate the cut error produced by the mismatch in velocity between the infeed product conveyor and the disc blade when uniformly advancing the infeed product conveyor. By eliminating this mismatch, a higher quality square cut is achieved.
The inventive saw uses the same skewed orbit axis as the '598 patent but provides a means for accelerating and decelerating the log during the short time period of the cutting cycle. Where the speed variation is between cuts, the roll cut length can be varied from the nominal, constant speed case. Even further, the means for accelerating and decelerating can be used to match the blade motion at the log. More particularly, variation of the inventive concept is where the log speed is non-uniform during cutting to match the actual, (sinusoidal) motion of the saw. According to the invention, a drive such as a servo motor is provided to vary the velocity of the product conveyor system on a continuous motion saw for achieving the objectives, i.e., solutions to problems, set forth above. Thus, in particular, the invention provides a means and method for correcting for chain wear. It provides a means and method for quick change of cutoff length and it provides a means and method for eliminating theoretical cut error due to mismatch in velocity between the blade and product during cutting.
Other objects and advantages of the invention may be seen in the details of construction and operation set down in the ensuing specification.